Optoelectronic arrangements are being used with ever-increasing frequency in commercial products or are close to market introduction. Such arrangements comprise organic or inorganic electronic structures, examples being organic, organometallic or polymeric semiconductors or else combinations of these. Depending on the desired application, the products in question are rigid or flexible in form, there being an increasing demand for flexible arrangements. Arrangements of this kind are frequently produced by printing techniques such as relief, gravure, screen or planographic printing or else by what is known as non-impact printing such as, for instance, thermal transfer printing, inkjet printing or digital printing. In many cases, however, vacuum techniques are used as well, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma-enhanced chemical or physical deposition techniques (PECVD), sputtering, (plasma) etching or vapor coating. Patterning generally takes place through masks.
Examples of optoelectronic applications that are already available commercially or are of interest in terms of their market potential include electrophoretic or electrochromic constructions or displays, organic or polymeric light-emitting diodes (OLEDs or PLEDs) in readout and display devices or as illumination, and also electroluminescent lamps, light-emitting electrochemical cells (LEECs), organic solar cells such as dye or polymer solar cells, inorganic solar cells, more particularly thin-film solar cells, based for example on silicon, germanium, copper, indium and selenium, organic field-effect transistors, organic switching elements, organic optical amplifiers, organic laser diodes, organic or inorganic sensors or else organic- or inorganic-based RFID transponders.
A perceived technical challenge for the realization of sufficient lifetime and function of optoelectronic arrangements in the area of organic and inorganic optoelectronics, especially of organic optoelectronics, is the protection of the components they contain against permeates. Permeates are generally considered to be gaseous or liquid substances which penetrate a solid body and may pervade it or migrate through it. Accordingly, numerous organic or inorganic compounds of low molecular mass may be permeates, with water vapor and oxygen being of particular significance in the context presently described.
A multiplicity of optoelectronic arrangements—especially where organic materials are used—are sensitive both to water vapor and to oxygen. During the lifetime of the electronic arrangements, therefore, protection is necessary through encapsulation, since otherwise there is a dropoff in performance over the application period. Otherwise, for example, oxidation of the constituents of light-emitting arrangements such as electroluminescent lamps (EL lamps) or organic light-emitting diodes (OLEDs) may drastically reduce the luminosity, the contrast in the case of electrophoretic displays (EP displays) or the efficiency in the case of solar cells, within a short time.
Within the field of inorganic and more particularly organic optoelectronics, therefore, there is a high demand for flexible adhesive bonding solutions which represent a barrier to permeates such as oxygen and/or water vapor. A number of approaches to such adhesive bonding solutions can already be found in the prior art.
Accordingly, with relative frequency, liquid adhesives and adhesive bonding agents based on epoxides are used as barrier adhesives, as are described in WO 98/21287 A1, U.S. Pat. No. 4,051,195 A and U.S. Pat. No. 4,552,604 A, for example. Their principal field of use is in edge bonds in rigid arrangements, but also moderately flexible arrangements. Curing takes place thermally or by means of UV radiation.
The use of these liquid adhesives is accompanied, however, by a series of unwanted effects as well. For instance, low molecular mass constituents (VOCs—volatile organic compounds) may damage the sensitive electronic structures of the arrangement and complicate production. The adhesive, furthermore, has to be applied, in a costly and inconvenient procedure, to each individual constituent of the arrangement. The acquisition of expensive dispensers and fixing devices is necessary in order to ensure precise positioning. The nature of the application has the effect, moreover, of preventing a rapid, continuous operation. In the laminating step that is subsequently necessary, the low viscosity may hinder the attainment of a defined film thickness and bond width.
An alternative is to use pressure-sensitive adhesives or hotmelt adhesives to seal optoelectronic constructions. Among the pressure-sensitive adhesives (PSAs) preference is given to using those which after bonding are crosslinkable by introduction of energy (for example, actinic radiation or heat). Adhesives of these kinds are described in US 2006/0100299 A1 and WO 2007/087281 A1 for example. Their advantage lies in particular in the fact that the barrier effect of the adhesives can be enhanced by crosslinking.
Also known in the prior art is the use of hotmelt (HM) adhesives. Used here in many cases are copolymers of ethylene, as for example ethylene-ethyl acetate (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-butyl acrylate (EBA) or ethylene-methyl acrylate (EMA). Crosslinking ethylene-vinyl acetate (EVA) copolymers are in general used more particularly for solar cell modules based on silicon wafers. Crosslinking takes place during the sealing operation under pressure and at temperatures of above around 120° C. For many optoelectronic constructions based on organic semiconductors or produced in thin-film processes, this operation is deleterious, as a result of the high temperatures and the mechanical load imposed by the pressure.
Hotmelt adhesives based on block copolymers or functionalized polymers are described in WO 2008/036707 A2, WO 2003/002684 A1, JP 2005-298703 A, and US 2004/0216778 A1, for example. An advantage of these adhesives is that the adhesives themselves do not introduce any substance—or only very little substance—into the construction to be encapsulated that itself harms the construction, whereas this problem is relevant particularly in the case of reactive liquid adhesive systems, more particularly those based on acrylate or on epoxy resin. In view of the high number of reactive groups, these systems have a relatively high polarity, and so, in particular, water is present therein. The amount is generally in the range of less than 100 ppm up to more than 1%. For this reason among others, such liquid adhesives are used primarily as an edge sealant for the electronic arrangements, where they are not in direct contact with the active electronic materials.
Another possibility for countering the problem of entrained permeates is to include additionally an absorbing material—called a getter—within the encapsulation, this getter binding—by absorption or adsorption, for example—water or other permeates that permeate through the adhesive or diffuse out of it. An approach of this kind is described in EP1407818 A1, US 2003/0057574 A1 and in US 2004-0169174 A1, among others.
Another measure is to equip the adhesive and/or the substrate and/or the cover of the electronic construction with such binding properties, as is described in WO 2006/036393 A2, DE10 2009 036 970 A1 and DE 10 2009 036 968 A1, for example.
It is possible, furthermore, to use raw materials with a particularly low permeate content or to free the adhesive from permeating substances during production or prior to application, by means, for example, of thermal drying, vacuum drying, freeze drying or the admixing of getters. Disadvantages of such methods are the long drying time and the possibly high or low drying temperatures, which may harm the adhesive or initiate chemical reactions, such as crosslinking for example. Moreover, the operation of admixing and subsequently removing the getters is costly and inconvenient.
Where such adhesive-related measures are taken to reduce the introduction of harmful permeating substances into the construction that is to be protected, it is necessary to maintain the properties produced with the minimum possible restriction, until the adhesive is used. Thus, for example, an adhesive which has been produced in a particularly anhydrous procedure must be protected from water uptake from the environment.
This problem is generally solved by providing the adhesives with packaging which is impervious to permeation or at least which inhibits permeation. Liquid adhesives are generally dispensed into corresponding containers, made of metal, for example. Adhesive tapes are often welded into flexible pouches made from permeation-inhibiting material—for example, from polyethylene film or from a film laminate of aluminum and polyester. The packaging materials themselves must also be very largely free from permeates that might be released on the contents side.
In order to counter weaknesses in the imperviosity of the packaging or to ensure rapid binding of permeates included, a getter is often included in the packaging as well, in the form for example of a pouch filled with silica gel or zeolite. This getter is generally not in direct contact with the contents. A particular disadvantage with this method is the increased cost and inconvenience of packaging.
A specific problem arises in the packaging of sheetlike adhesives, i.e., adhesive tapes or adhesive sheets: when they are stacked as shapes or wound to form a roll, gas—air, for example—is included, which is not in exchange with the rest of the gas space remaining in the packaging. Unwanted permeates present, for example water vapor, therefore do not reach the getter material located in the packaging, and may therefore migrate into the adhesive. Furthermore, such adhesive tapes generally include a temporary liner material, and also often a carrier material as well. These materials may likewise comprise unwanted permeates, which may easily permeate into the adhesive in view in particular of the large area of contact with said adhesive. Getter pouches or getter pads introduced into the packaging may not reliably scavenge and bind these permeates. Freeing the liner materials and carrier materials entirely from the unwanted permeates, by means of drying, for example, is laborious, costly and inconvenient.
EP 2 078 608 A1 discloses the use of liner materials which comprise a special permeation barrier. This approach, however, is not effective against permeates present in the liner or included between liner and adhesive.
There is therefore an ongoing need for liners which reliably protect a sheetlike adhesive from the influence of permeates.
It is an object of the present invention, therefore, to provide a liner which protects an adhesive not only from permeates originating from the environment but also from permeates included in the course of winding or stacking and other processing steps. Accordingly, in the case of a product, such as an adhesive tape, which comprises a largely permeate-free adhesive layer, this adhesive layer is to be kept largely free from permeates for the period of storage and of transport, with the adhesive layer preferably in fact being freed from remaining permeates as well.
The achievement of this object derives from the fundamental concept of the present invention, namely providing a liner with getter materials contained therein.